1. Field of the Invention
The present invention relates to a process for preparing tungsten hexafluoride from selected tungsten compounds, a halogen and hydrogen fluoride.
2. Prior Art
Tungsten hexafluoride is used when plating with tungsten, in certain welding operations, and for numerous other known uses. It has heretofore been prepared directly by the reaction of elemental fluorine with metallic tungsten, a process which is prohibitively expensive, requires highly skilled personnel and specialized equipment.
Tungsten hexafluoride may also be prepared by the reaction set forth in U.S. Pat. No. 3,185,543, namely, by reacting tungsten with NOF.sup.. 3 HF complex, but this is an indirect route since the NOF.sup.. 3 HF complex must first be prepared by reacting nitrosyl chloride with HF.
U.S. Pat. No. 3,373,000 to Jache et al sets forth a process for preparing tungsten hexafluoride from chlorine monofluoride and discloses other interhalogen compounds which may be employed as fluorinating agents. Each of these routes is also indirect in that the fluorinating agent is not a readily available commodity chemical and must therefore be prepared as part of the overall process of preparing tungsten hexafluoride. In the case of chlorine monofluoride, U.S. Pat. No. 3,451,775 sets forth a process by which this interhalogen may be prepared.
It is extremely desirable to avoid the indirect routes described above, to avoid the use of elemental fluorine, and to find a direct route to tungsten hexafluoride which utilizes inexpensive and readily available starting materials.
It has now been found that these and other advantages may be attained by reacting a selected tungsten compound, a halogen and hydrogen fluoride at elevated pressure and at a temperature of 150.degree. C.-150.degree. C. under anhydrous conditions in the absence of air.